Strees Corrosion Cracking Initiation of Ni-Bassed Alloys in High Temperature Water Page: 4 of 15
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DC Electrical Potential Drop (EPD) to Measure Initiation
HP Ctr4 A
R = AV/1 = pL/A Av
In Plastic Regime Volume is
R = (p/Vo)(Lo+AL)2=
(pLo2/Vo)(1 +AL/ Lo)2
Strain, E = (R/R0)1/2 1 HP
Strain is related to change in resistance due to SCC initiation
DC electric potential drop is used to measure the stress corrosion cracking
(SCC) initiation time. A constant DC current is passed through the specimen
and the voltage difference between probes on each end of the gage length is
measured. The current distribution is uniform, thus the voltage difference
between the two probes is proportional to the distance between the probes
and inversely proportional to the cross-sectional area of the gage region.
Formation of SCC reduces the gage cross-sectional area and causes an
increase in the voltage difference between the two probes. This increase in
voltage signifies SCC initiation. The voltage measured on the test specimen
is normalized for temperature and material resistivity changes with a voltage
measured from a "reference" specimen of the same material. The
"reference" specimen is pre-strained at the test temperature to the same
load as the test specimen prior to testing, but it is not under any load during
the test. SCC has not occurred in any of these non-loaded pre-strained
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Richey, E & Morton, D. Strees Corrosion Cracking Initiation of Ni-Bassed Alloys in High Temperature Water, article, March 21, 2005; Niskayuna, NY. (https://digital.library.unt.edu/ark:/67531/metadc880365/m1/4/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.